Maybe this is naive, but the younger you are, the larger the ratio of each unit of time to your total time lived. So each unit of time seems longer.
I agree with both the "ratio" and "routine" arguments.
Speaking of getting older, what's with the incredibly tiny fonts on web sites these days? I can read it OK, but Ctrl + makes it less annoying. If they're trying to "fit more ads" it's backfiring in my case because I'm less likely to read it. Now get off my lawn.